1. Field of the Invention
The present invention relates to a method for assembling semiconductor switching elements and a heat sink in a rotary electric machine which is mounted in a limiting space such as an electric automobile, a hybrid vehicle, an idling stop vehicle or the like and a rotary electric machine.
2. Description of the Related Art
Recently, to achieve the prevention of global warming, the reduction of CO2 emission is requested. Particularly, an electric automobile, a hybrid vehicle and an idling stop vehicle which can enhance the mileage performance by the idling stop at the time of stopping a vehicle, the regeneration of energy during the deceleration traveling and the torque assisting during the acceleration traveling have been developed and put into practice.
As described in Japanese Patent Laid-open Hei 8(1996)-289505 (see FIG. 1 to FIG. 5 and explanation thereof), in the control device structure in a control-device integral-type motor which includes semiconductor switching elements, the semiconductor switching elements are mounted on a substrate on which a circuit pattern is formed and is basically formed of metal having a high heat radiation property while including an insulation layer.
Further, the above-mentioned substrate is, for enhancing the cooling performance, mounted on a heat sink using bolts by way of grease to enhance the cooling property.
In general, in the inside of the control device, as shown in FIG. 11, packaged semiconductor switching elements 41P are bonded to a metal substrate 600 which is constituted of a metal base plate made of Al or the like, a pattern 600a made of copper or the like, an insulation layer 600b and a metal base plate 600c by soldering 52. The semiconductor switching elements 41P are configured such that chips are connected to a heat spreader and the chips are individually packaged with a resin. The metal substrate 600 on which the packaged semiconductor switching elements 41P are mounted is connected to the heat sink 50 using bolts by way of grease 601.
For example, to illustrate a case of the control-device integral-type electrically-operated generator for an automobile, there exist following kinds of drawbacks to be solved.
In connecting a motor control device and the electrically-operated generator, when the control device and the electrically-operated generator are separated from each other, particularly, when the control device and the electrically-operated generator are largely separated from each other, a wiring length is increased and hence, a wiring resistance is increased thus giving rise to a large voltage drop whereby it is difficult to obtain desired torque characteristics and a rotational speed.
Further, the elongation of the wiring gives rise to drawbacks such as the increase of weight and the increase of cost.
In a limited installation space such as the inside of an engine room or the like, it is extremely difficult to ensure a space for installing the electrically-operated generator and, at the same time, to incorporate the control device in the inside of the electrically-operated generator, it is necessary to miniaturize the whole structure of the control device.
In the inside of the control device, it is necessary to cool the semiconductor elements having a large heat value such as power semiconductor switching elements for a main circuit or the like and hence, a heat sink (a radiator) for cooling the semiconductor elements becomes large-sized and substantially occupies a major portion of a volume of the control device. To cope with the high output specification which is expected in future, the heat sink size is increased and the heat sink may not be accommodated in the inside of the electrically-operated generator.
Conventionally, the semiconductor elements are mounted on the metal substrate and, thereafter, the metal substrate is mounted on the heat sink by way of grease. Since the insulation layer having small heat conductivity is interposed in the inside of the substrate, the heat resistance is increased and the heat radiation is extremely lowered. To cope with such a situation, it is necessary to increase the size of the heat sink and this makes it difficult to accommodate the heat sink in the inside of the electrically-operated generator.
Further, the semiconductor elements used in the electrically-operated generator exhibit a particularly large loss quantity and consume large heat content. The metal substrate contains silica as a filler in a portion of an insulation material and also uses other high-grade material thus pushing up a manufacturing cost.
Further, since the substrate is mounted on the heat sink, a grease coating step, a fixing step using bolts and the like become necessary thus exhibiting the poor productivity.
When the semiconductor elements are directly mounted on the heat sink, the heat sink forms electrodes and it is difficult to ensure the insulation against the respective electrodes.
Further, the connection and the wiring of the semiconductor elements with surrounding part connecting portions become complicated and difficult.
It is necessary to enhance the productivity and, at the same time, it is necessary to acquire the reduction of cost.